1. Field of the Invention
The present invention relates to phased array antenna arrangements which use frequency multiplication to reduce the number of required phase shifters and, more particularly, to phased array antenna arrangements which launch a desired directional wavefront at a much lower frequency than desired using only the number of feed elements and associated phase shifters needed to launch such low frequency beams in a predetermined direction, and then separately harmonically upconverting and amplifying, if necessary, the low frequency beam signals found at an image plane of the low frequency beam launching array, with the originally generated phase shifts, to the actual transmission frequency and level for launching in the desired directional output beam.
2. Description of the Prior Art
In order to prevent grating lobes from appearing in the field of view of a phased array antenna, the phased array must have N x M elements, where N is approximately the number of beamwidths in the field of view in one plane and M is that in the orthogonal plane. Each of these elements requires a phase shifter which must be individually adjusted to aim the phased array antenna beam anywhere in the field of view. Conventional arrays of this type generally require a large number of phase shifters which may be inappropriate in certain applications as, for example, a satellite scanning beam phased array antenna where factors of complexity, weight, maintenance, aperture size and range of scanability are important factors.
U.S. Pat. No. 3,576,579 issued to A. J. Appelbaum et al on Apr. 27, 1971 attempts to overcome certain of the above-stated factors by providing a planar radial array with a controllable quasi-optical lens which includes a radial line power-dividing means. In accordance with the Appelbaum et al patent, a power feed apparatus is provided which includes a power-dividing means and a power-distributing means. The power-dividing means includes an input port and n output ports and is operative to receive an input signal of a predetermined power level at the input port and to divide the input signal into n output signals of reduced power level at the n output ports. The power-distributing means is operative to receive the n output signals from the n output ports of the power-dividing means and to provide m output signals of varying power levels at m output connections. When the above-described power-dividing and power-distributing apparatus is employed in a power feed apparatus for a phased-array antenna system, the m output signals of varying power levels are used to establish the required power levels for the antenna elements of the array whereby a desired beam taper illumination function is achieved across the aperture defined by the array of antenna elements. The Appelbaum et al arrangement, however, still requires a reasonably large number of feed elements and associated phase shifters.
U.S. Pat. No. 3,835,469 issued to C. C. Chen et al on Sept. 10, 1974 relates to an optical limited scan antenna system including an aperture lens, a feed lens and a feed array for scanning a pencil beam or multiple simultaneous beams over a limited angular sector with good sidelobe levels and minimum gain degradation. Both amplitude and phase distributions over the aperture lens are controlled for all scan angles. In accordance with the Chen et al arrangement, an aperture lens that is large in diameter compared with that of a feed lens is placed in confocal relationship therewith. Both the aperture and feed lens are entirely passive and are focused by means of fixed phase shifters or line lengths in the elements. A small phased array or other source is used to illuminate a portion of the feed lens with a plane wave segment. This wave passes through the feed lens, converges near the broadside focus at the focal plane, then spreads out again and is intercepted by the aperture lens which refocuses the energy to infinity. By changing the angle of the plane wave emanating from the small feed antenna, the beam is scanned in the far field.
U.S. Pat. No. 3,631,503 issued to R. Tang et al on Dec. 28, 1971 relates to a high performance distributionally integrated subarray antenna which consists of a feed-through lens with a high-performance feed system. The Tang et al arrangement employs the technique of resolving the radiating array of the feed-through lens into subarrays which overlap each other completely over the entire radiating aperture. Each of the subarrays has a truncated sinx/x amplitude distribution across the entire radiating aperture where x is linear distance therealong, thus producing a radiation pattern closely rectangular in shape. The rectangular subarray pattern is stated as being ideal, since it maximizes the array gain and minimizes the grating lobe level for a given system bandwidth. Therefore, this overlapping subarray technique supposedly allows the antenna to perform over a wide instantaneous bandwidth with a minimum number of subarrays or time delay phase shifters. Use of this technique also supposedly tends to minimize cost, since the cost of such a system is reflected in the number of subarrays required. This arrangement, however, requires a reasonably large number of feed elements and associated phase shifters in the feed-through lens to provide adequate scanning capabilities and correcting for the spherical aberration of the lens.
The problem remaining in the prior art is to provide a phased array antenna arrangement which provides wide field of view scanning with reduced numbers of feed elements and associated phase shifters than normally used with conventional phased array antennas having comparable capabilities.